Is it a breach of contract to delay paying the rent for one or two days?

Delaying the payment of rent does not meet the contractual obligations and is a breach of contract.

Contract law:

Article 113 Where a party fails to perform its contractual obligations or fails to perform its contractual obligations in conformity with the contract, thus causing losses to the other party, the amount of compensation shall be equivalent to the losses caused by the breach of the contract, including the benefits that can be obtained after the performance of the contract, but shall not exceed the losses that the breaching party foresaw or should have foreseen when concluding the contract.

Operators who provide commodities or services to consumers are fraudulent shall be liable for damages in accordance with the provisions of the Law of People's Republic of China (PRC) on the Protection of Consumer Rights and Interests.